The present invention relates to a thermoelectric device which cools or heats a member by using a thermoelectric element having one surface on the low temperature side and the other surface on the high temperature side.
Conventionally, as a humidity measuring method, a dew point detection method is known, in which the temperature of a target measurement gas is decreased, and the temperature at which vapor contained in the target measurement gas partially condenses is measured, thereby detecting the dew point. For example, reference 1 (“The Outline of Industrial Measurement Technology 10, Temperature/Moisture Measurement”, Nikkan Kogyo Shimbun, PP. 87-91) describes a mirror surface cooling dew point detector which cools a mirror by using a freezing mixture, refrigerator, or electronic cooler, detects a change in intensity of reflected light on the mirror surface of the cooled mirror, and measures the temperature of the mirror surface at this time, thereby detecting the dew point of moisture in the target measurement gas.
Mirror surface cooling dew point detectors are classified into two types depending on the type of reflected light to be used. One type uses a regular-reflected light detection method using regular-reflected light described in reference 2 (Japanese Patent Laid-Open No. 61-75235). The other type uses a scattered light detection method using scattered light described in reference 3 (Japanese Patent Laid-Open No. 63-309846).
[Regular-Reflected Light Detection Method]
FIG. 26 shows the main part of a conventional mirror surface cooling dew point detector which employs the regular-reflected light detection method. A mirror surface cooling dew point detector 101 comprises a chamber 1 in which a target measurement gas flows and a thermoelectric cooling element (Peltier element) 2 provided in the chamber 1. A bolt 4 is attached to a cooled surface 2-1 of the thermoelectric cooling element 2 through a copper block 3. A radiating fin 5 is attached to a heated surface 2-2 of the thermoelectric cooling element 2. An upper surface 4-1 of the bolt 4 attached to the copper block 3 is a mirror surface. A hole is formed in the side surface of the copper block 3. A wire-wound resistance thermometer sensor (temperature detection element) 6 is embedded in this hole through silicone grease (FIG. 28). A light-emitting element 7 which obliquely irradiates the upper surface (mirror surface) 4-1 of the bolt 4 with light and a light-receiving element 8 which receives the regular-reflected light of light emitted from the light-emitting element 7 to the mirror surface 4-1 are provided at the upper portion of the chamber 1.
In the mirror surface cooling dew point detector 101, the mirror surface 4-1 in the chamber 1 is exposed to the target measurement gas flowing into the chamber 1. If no condensation occurs on the mirror surface 4-1, the light emitted from the light-emitting element 7 is almost wholly regularly reflected and received by the light-receiving element 8. Hence, when no condensation occurs on the mirror surface 4-1, the intensity of reflected light received by the light-receiving element 8 is high.
As the current to the thermoelectric cooling element 2 is increased to lower the temperature of the cooled surface 2-1 of the thermoelectric cooling element 2, vapor contained in the target measurement gas condenses on the mirror surface 4-1. The light emitted from the light-emitting element 7 is partially absorbed or diffused by the molecules of water. The intensity of the reflected light (regular-reflected light) received by the light-receiving element 8 decreases. When the change in regular-reflected light on the mirror surface 4-1 is detected, the change of the state on the mirror surface 4-1, i.e., adhesion of moisture (water droplets) on the mirror surface 4-1 can be recognized. In addition, when the temperature of the mirror surface 4-1 at this time is measured indirectly by the temperature detection element 6, the dew point of moisture in the target measurement gas can be detected.
[Scattered Light Detection Method]
FIG. 27 shows the main part of another conventional mirror surface cooling dew point detector which employs the scattered light detection method. A mirror surface cooling dew point detector 102 has almost the same arrangement as the mirror surface cooling dew point detector 101 using the regular-reflected light detection method except the mount position of the light-receiving element 8. In the mirror surface cooling dew point detector 102, the light-receiving element 8 is provided not at the position to receive the regular-reflected light of light emitted from the light-emitting element 7 to the mirror surface 4-1 but at the position to receive scattered light.
In the mirror surface cooling dew point detector 102, the mirror surface 4-1 is exposed to the target measurement gas flowing into the chamber 1. If no condensation occurs on the mirror surface 4-1, the light emitted from the light-emitting element 7 is almost wholly regularly reflected, and the amount of light received by the light-receiving element 8 is very small. Hence, when no condensation occurs on the mirror surface 4-1, the intensity of reflected light received by the light-receiving element 8 is low.
As the current to the thermoelectric cooling element 2 is increased to lower the temperature of the cooled surface 2-1 of the thermoelectric cooling element 2, vapor contained in the target measurement gas condenses on the mirror surface 4-1. The light emitted from the light-emitting element 7 is partially absorbed or diffused by the molecules of water. The intensity of the diffused light (scattered light) received by the light-receiving element 8 increases. When the change in scattered light on the mirror surface 4-1 is detected, the change of the state on the mirror surface 4-1, i.e., adhesion of moisture (water droplets) on the mirror surface 4-1 can be recognized. In addition, when the temperature of the mirror surface 4-1 at this time is measured indirectly by the temperature detection element 6, the dew point of moisture in the target measurement gas can be detected.
In the above-described dew point detectors, condensation (moisture) on the mirror surface 4-1 is detected. With the same arrangement as described above, frost (moisture) on the mirror surface 4-1 can also be detected.
However, for the above-described conventional mirror surface cooling dew point detector 101 or 102, assembly is not easy because the temperature detection element 6 is embedded through the silicone grease in the hole formed in the side portion of the copper block 3. Since the temperature detection element 6 is covered with the silicone grease, the response is poor due to the thermal resistance by the silicone grease. The copper block 3 is inserted between the mirror surface 4-1 and the thermoelectric cooling element 2. With this structure, a temperature gradient which decreases the measurement accuracy may be generated. In addition, since the thermal capacity by the copper block 3 is large, and the response is poor. Since the copper block 3 is provided, the outer size of the sensor unit increases, and size reduction is difficult.
Reference 4 (Japanese Patent Laid-Open No. 9-307030) describes a cooling device which cools a heat-producing electronic device (e.g., CPU) by using a thermoelectric cooling element. In this cooling device, the CPU is attached to the cooled surface of the thermoelectric cooling element, and the temperature of the semiconductor element or cooling-side conductor of the thermoelectric cooling element is measured. More specifically, as shown in FIG. 29, a CPU (cooled member) 61 is attached to the cooled surface 2-1 of the thermoelectric cooling element 2. A temperature detection element 62 is attached to a column (semiconductor element) 2a of the thermoelectric cooling element 2 or a bottom surface 2b of the cooled surface (cooling-side conductor) 2-1 to indirectly measure the temperature of the CPU 61. An arrangement can be considered from the structure described in reference 4, in which a mirror 9 is attached to the cooled surface 2-1 of the thermoelectric cooling element 2, and the temperature detection element 62 measures the temperature of the column 2a of the thermoelectric cooling element 2 or the bottom surface 2b of the cooled surface 2-1, as shown in FIG. 30. In this structure, however, since a thermal resistance is generated in the bonding portion between the mirror 9 and the cooled surface 2-1 of the thermoelectric cooling element 2 and in the cooled surface 2-1 itself, the temperature of the mirror 9 cannot be detected accurately at a satisfactory response.
Although mirror surface cooling dew point detectors have been described above, this also applied to the conventional cooling device shown in FIG. 29. That is, the temperature of the CPU 61 cannot accurately be detected. As shown in FIG. 31, a member 63 is attached to the heated surface 2-2 of the thermoelectric cooling element 2 and heated. In this case, the thermoelectric cooling element 2 serves as a thermoelectric heating element so that not a cooling device but a heating device is formed. Even in this case, when the temperature of the column 2a of the thermoelectric heating element 2 or a bottom surface 2c of the heated surface 2-2 is measured, the temperature of a member (heated member) 30 cannot be detected accurately at a high response. The thermoelectric cooling element 2 will also be referred to as a thermoelectric heating element depending on its utilization form, and “thermoelectric element” will be used as a general term for the thermoelectric cooling element and thermoelectric heating element hereinafter.